Atomic Structure and The Periodic Table (review)

1. Manganese sulfide is a naturally occurring compound of manganese. The figure below shows the structure for manganese sulfide.

a) Use this infromation to determine the formula of manganese sulfide.

Answer: MnS

b) Manganese is found in the central block of the periodic table. It has an atomic number of 25 and a mass number of 55. What type of metal is manganese?

Answer: Manganese is a transition metal.

c) Give the number of protons, neutrons and electrons in an atom of manganese.

Answer: 25 protons, 30 neutrons, 25 electrons

d) Give three typical chemical properties of manganese, based on its position in the periodic table.

Answer: reacts to form ions with different charges ; forms coloured compounds ; it (or its compounds) has catalytic properties ; generally low reactivity

e) Sulfur is a non-metal in Group 6 of the periodic table. The atomic number of sulfur is 16. Give the electron arrangement for an atom of sulfur.

Answer: 2-8-6

f) When sulfur atoms react they tend to gain two electrons to form sulfide ions, S2−. Explain why sulfide ions have a 2–  charge. Answer in terms of sub-atomic particles.

Answer: Sulfide ions have 16 protons and 18 electrons. The total positive charge is 16+ and the total negative charge is 18– . So the overall charge is 2− .

2. Atomic theory has developed over time from a very simple model of the atom to the more complicated one that we use today. The following list of terms are all related to atoms and sub-atomic particles: nucleus, protons, neutrons, electrons and electron shells.

a) Which structure is most associated with the work of Neils Bohr? Choose one word from the list.

Answer: electron shells

b) Which particle is most associated with the work of James Chadwick? Choose one word from the list.

Answer: neutrons

c) Which structure is most associated with the work of Ernest Rutherford? Choose one word from the list.

Answer: nucleus

d) The figure below is a representation of the alpha particle scattering experiment carried out by Hans Geiger and Ernest Marsden. Use this information and your own knowledge to describe how evidence from the scattering experiment led to a change in the atomic model.

Answer: The plum-pudding model of the atom described atoms as balls of positive charge with negatively charged electrons spread through them. The results from the scattering experiment could not be explained by the plum-pudding model. The results proved that atoms had a tiny, positively charged nucleus. This led to the development of the nuclear model of the atom.

3. The halogens are elements in Group 7 of the periodic table.

a) Describe the relationship between the relative molecular mass and boiling points of the Group 7 elements.

Answer: As the relative molecular mass of the elements increases, their boiling point increases.

b) When bromine reacts with iron, the compound iron bromide, FeBr3 is formed. Give the balanced equation for this reaction.

Answer: 2Fe + 3Br2  →  2FeBr3

c) When iodine reacts with iron the reaction releases less energy and occurs much more slowly than the reaction of bromine and iron. Compare these two reactions. Use your knowledge to explain each of their similarities and differences.

Answer: Iodine reacts in a similar way to bromine because it has the same number of outer-shell electrons as bromine. Iodine is less reactive than bromine. When halogens react they gain one electron to fill their outer-shell of electrons. Iodine atoms will have more electron shells than bromine atoms, so the gained electron is further from the nucleus in iodine. This means the electron is less strongly attracted to the iodine nucleus, and is harder to gain. This makes iodine less reactive.

d) Name the products formed when chlorine reacts with a solution of iron bromide.

Answer: iron chloride and bromine

e) Name a suitable method for separating soluble iron bromide from its solution.

Answer: crystallisation or evaporation

4. The alkali metals make up Group 1 of the periodic table.

a) Explain why the alkali metals are found in Group 1 of the periodic table.

Answer: They all have one electron in their outer shells.

b) Explain how it is possible to know that sodium is a metal and chlorine is a non-metal. You should make reference to the elements’ positions in the periodic table, as well as the ions formed when the elements react.

Answer: Sodium is on the left-hand side of the periodic table, whilst chlorine is on the right-hand side. When sodium atoms react they form positive ions (by losing their one outer-shell electron). When chlorine atoms react they form negative ions (by gaining one outer-shell electron).

c) The alkali metals react readily with water. Name the two products that form when sodium reacts with water.

Answer: sodium hydroxide and hydrogen

d) Lithium metal reacts less vigorously with water than sodium. Explain why lithium is less reactive than sodium.

Answer: When Group one metals react they lose their one outer-shell electron. Lithium has fewer electron shells than sodium so the outer-shell electron is closer to the nucleus and more strongly attracted to it. This makes it harder for the electron to be lost, so lithium is less reactive.

5. The figure below shows part of Newlands’ periodic table.

a) Suggest why Newlands grouped the elements into columns.

Answer: Because the elements had similar properties.

b) Explain why Newlands’ periodic table was not widely accepted by other chemists of the time.

Answer: Newlands’ groupings stopped working after the first 20 elements or so. For instance, he placed iron, a metal, together with oxygen and sulfur, which are non-metals.

c) The figure below shows part of Mendeleev’s periodic table. Suggest why the Group 0 elements do not appear in either Newlands’ or Mendeleev’s periodic tables.

Answer: Group 0 elements are very unreactive, so had not been discovered at that time.

d) Explain how Mendeleev’s periodic table was an improvement upon Newlands’ periodic table and why his ideas were more widely accepted.

Answer: Mendeleev left gaps in his periodic table for elements that had not been discovered yet. He also swapped the positions of some elements to better suit their properties. Mendeleev made predictions about the undiscovered elements. When new elements were discovered that matched Mendeleev’s predictions his periodic table became widely accepted.